Characterization and Identification of the most Refractory Nitrogen Compounds in Hydroprocessed Vacuum Gas Oil

Abstract

There is currently a growing need to hydroprocess heavier and tougher crude oils with increased nitrogen content. Therefore, hydrodenitrogenation (HDN) has become a critical hydroprocessing reaction, making it essential to gain insight into which nitrogen-containing compounds are the most difficult to treat. In the present article, we describe the identification of nitrogen compounds in severely pretreated feed for hydrocracking (HC). The nitrogen compounds in the N-slip to the hydrocracker are isolated and concentrated on solid-phase extraction (SPE) columns and identified by gas chromatography mass spectrometry (GC-MS), gas chromatography with atomic emission detection (GC-AED), and nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculations support the structural identification and are further used to investigate the reactivity. We find that the most refractory organic nitrogen compounds in the N-slip belong to the family of 4,8,9,10-tetrahydrocyclohepta[def]carbazoles. These molecules are slightly more basic than other carbazoles and thus are likely to have an impact on the performance of the downstream catalysts; however, their very low reactivities make them extremely difficult to remove under normal hydrotreating conditions.

Structural Analysis of Neutral Nitrogen Compounds Refractory to the Hydrodenitrogenation Process of Heavy Oil Fractions by High-Resolution Tandem Mass Spectrometry and Ion Mobility–Mass Spectrometry

“…The nitrogen hydrotreating process, called HDN, is used as a nitrogen removal process, which is typically carried out prior to the hydrodesulfurization process . Nitrogen removal requires the saturation of an aromatic ring adjacent to the nitrogen atom. − Some of these nitrogen compounds are resistant to HDN processes; they are called refractory molecules. Molecular characterization of complex mixtures, such as petroleum products, is challenging and generally involves the use of sophisticated methodologies with high resolution and separation capabilities.…”

Feasibility of Bitumen Production from Unconverted Vacuum Tower Bottom from H-Oil Ebullated Bed Residue Hydrocracking

“…The same is observed with nitrogen content. The concentration of nitrogen-containing compounds in UVTB is connected with increased conversion in the H-Oil unit as their very low reactivity makes them extremely difficult to convert. Simultaneously, Figure points out the dependence of penetration on conversion, and the nitrogen content can be correlated to penetration via conversion (due to reactor temperatures) of the ebullated bed hydrocracking process.…”

Insights from Nitrogen Compounds in Gas Oils Highlighted by High-Resolution Fourier Transform Mass Spectrometry

“…However, it can be stated that 150 ppm of carbazoles remained in sample after deep hydrotreatment that corresponds to almost half of the initial concentration of carbazoles, validating the wellknown refractory character of these molecules. 36,37 The evolutions of RINNC for carbazoles molecules for each possible DBE (9, 10, and 11) were different according to DBE value as seen in Figure 5B. Carbazoles with a DBE value of 10 were revealed to be the most refractory as 50% were still remaining in HDT 2, whereas only 40% and 30% remained in HDT 2 for DBE 9 and DBE 11 respectively.…”